Laminated Polyester Film

Abstract

To provide a laminated polyester film which suppresses precipitation of an oligomer, and is excellent in blocking resistance.SOLUTION: A laminated polyester film includes a coating layer on at least one surface of a polyester film, wherein a surface elastic modulus of the coating layer exceeds 6.0 GPa or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a laminated polyester film. [Background technology]

[0002] Polyester films have excellent properties such as mechanical strength, dimensional stability, flatness, heat resistance, chemical resistance, optical properties, and the like, and also have excellent cost performance, so they are used as base films for packaging materials, plate-making materials, display materials, transfer materials, and the like.

[0003] In these applications, a functional layer such as a hard coat layer is often formed on the surface of the polyester film, which is the base film, in order to improve scratch resistance and surface hardness and to prevent curling. However, most substrate films are non-reactive, and the adhesion between the substrate film and the functional layer may be insufficient. Therefore, in order to improve the adhesion between the substrate film and the functional layer, a highly adhesive coating layer is generally provided as an intermediate layer.

[0004] For example, Patent Documents 1 and 2 disclose a method of coating a water-soluble or water-dispersible coating liquid of polyurethane resin, polyester resin, acrylic resin, or the like onto a substrate film. However, under conditions of high temperature and high humidity, the adhesion between the highly adhesive coating layer and the base film and / or functional layer tends to be insufficient.

[0005] In view of the above circumstances, methods are known in which the adhesiveness under high temperature and high humidity conditions is improved by crosslinking the resin, as disclosed in Patent Documents 3 and 4. Specifically, by adding a crosslinking agent such as a melamine compound, an epoxy compound, or an oxazoline compound to the polyurethane resin, polyester resin, or acrylic resin that forms the coating layer, the adhesion to the base film and / or the functional layer can be improved. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 55-15825 [Patent Document 2] Japanese Patent Application Publication No. 58-78761 [Patent Document 3] Japanese Patent Application Publication No. 8-281890 [Patent Document 4] Japanese Patent Application Publication No. 11-286092 Summary of the Invention [Problem to be solved by the invention]

[0007] However, when the coating layer is produced at a high temperature in order to advance the curing reaction of the crosslinking agent in the coating layer, oligomers (mainly cyclic ester trimers) precipitate from the substrate film, and during the roll-form production process, the oligomers precipitated from the substrate film may adhere to the surface of the coating layer. On the other hand, when the film was produced at a low temperature in order to suppress the amount of oligomers precipitating from the base film, depending on the composition in the coating layer, the curing reaction did not proceed sufficiently, and during the processes of production, processing, storage, etc., when the laminated polyester film was wound into a roll, blocking such as films sticking together could occur. Thus, it may be difficult to simultaneously suppress oligomer precipitation and improve blocking resistance. In view of the above circumstances, an object of the present invention is to provide a laminated polyester film which inhibits oligomer precipitation and has excellent blocking resistance. [Means for solving the problem]

[0008] As a result of extensive investigations, the present inventors have found that by increasing the surface elastic modulus of the coating layer above a specific value, not only can the precipitation of oligomers be suppressed but also blocking resistance can be improved, thereby solving the above-mentioned problems. The present invention has been completed based on these findings and has the following aspects. [1] A laminated polyester film having a coating layer on at least one side of the polyester film, the coating layer having a surface elastic modulus of more than 6.0 GPa. [2] The laminated polyester film according to [1] above, wherein the coating layer has a surface hardness of 370 MPa or more. [3] The laminated polyester film according to the above [1] or [2], wherein the coating layer is formed from a coating liquid containing a crosslinking agent (A) that contains an epoxy compound (A1). [4] The laminated polyester film according to the above [3], wherein the crosslinking agent (A) further contains an oxazoline compound (A2), and a content ratio (A1) / (A2) of the epoxy compound (A1) to the oxazoline compound (A2) is 80 / 20 to 20 / 80. [5] The laminated polyester film according to any one of the above [1] to [4], wherein the coating liquid further contains an acid catalyst (C). [6] The laminated polyester film according to the above [5], wherein the acid catalyst (C) has a sulfonic acid group or a phosphoric acid group. [7] The laminated polyester film according to the above [5] or [6], wherein the acid catalyst (C) is at least one selected from the group consisting of p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid, dinonylnaphthalene (mono)sulfonic acid, and dodecylbenzenesulfonic acid. [8] The laminated polyester film according to any one of the above [1] to [7], wherein the coating liquid further contains a binder resin (B), and the binder resin (B) contains a polyester resin. [9] The laminated polyester film according to any one of the above [1] to [8], which has a micro heat of fusion peak temperature of 160°C or higher and 210°C or lower.

[10] A laminated polyester film having a functional layer, comprising the laminated polyester film according to any one of the above [1] to [9] and a functional layer on the coating layer.

[11] The laminated polyester film with a functional layer according to the above

[10] , wherein the functional layer is a hard coat layer. Effect of the Invention

[0009] INDUSTRIAL APPLICABILITY According to the present invention, a laminated polyester film which inhibits oligomer precipitation and has excellent blocking resistance is provided, and the film is highly useful in industrial applications. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An example of an embodiment of the present invention will be described in detail below. However, the present invention is not limited to the embodiment described below, and can be modified in any manner without departing from the gist of the present invention.

[0011] The laminated polyester film of the present invention has a coating layer on at least one side of a polyester film, and the coating layer has a surface elastic modulus of more than 6.0 GPa. Each of the constituent elements will be described in detail below.

[0012] <Polyester film> The polyester film constituting the laminated polyester film in the present invention may have a single-layer structure or a multi-layer structure. When the polyester film has a multi-layer structure, the polyester film may have a two-layer structure, a three-layer structure, etc., or may have four or more layers without departing from the gist of the present invention, and the number of layers is not particularly limited. The polyester film may be a non-stretched film (sheet) or a stretched film. Of these, a uniaxially or biaxially stretched film is preferable. Of these, a biaxially stretched film is more preferable from the viewpoints of balance of mechanical properties, flatness, and thinning.

[0013] The polyester used as the raw material for the polyester film may be either a homopolyester or a copolymer polyester. In the case of a homopolyester, it is preferable that the homopolyester is obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of aromatic dicarboxylic acids include terephthalic acid, 2,6-naphthalenedicarboxylic acid, and esters thereof (e.g., dimethyl terephthalate), and examples of aliphatic glycols include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. A representative example of homopolyesters is polyethylene terephthalate. On the other hand, examples of the dicarboxylic acid component of the copolymer polyester include one or more of isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid, oxycarboxylic acid, etc., and examples of the glycol component include one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, 4-cyclohexanedimethanol, neopentyl glycol, etc., provided that at least one of the dicarboxylic acid component and the glycol component is used in two or more kinds.

[0014] The polyester polymerization catalyst is not particularly limited, and any conventionally known compound can be used, such as titanium compounds, germanium compounds, antimony compounds, manganese compounds, aluminum compounds, magnesium compounds, and calcium compounds.

[0015] In order to suppress the amount of precipitation of oligomer components, the film may be produced using a polyester having a low content of oligomer components as the raw material. As a method for producing a polyester having a low content of oligomer components, various known methods can be used, such as a method of performing solid phase polymerization after the production of a polyester. The amount of precipitation of oligomer components may be suppressed by forming the polyester film into a three-layer or more layer configuration and using a polyester raw material having a low content of oligomer components as the outermost layer of the polyester film. The polyester may be obtained by carrying out the esterification or transesterification reaction, followed by melt polycondensation at a higher reaction temperature under reduced pressure.

[0016] The polyester film may contain an ultraviolet absorbing agent in order to improve the weather resistance of the film and prevent deterioration of the adherend (e.g., liquid crystal), etc. The ultraviolet absorbing agent is a compound that absorbs ultraviolet light and is not particularly limited as long as it can withstand the heat applied in the manufacturing process of the polyester film.

[0017] The ultraviolet absorbing agent includes organic ultraviolet absorbing agents and inorganic ultraviolet absorbing agents, and from the viewpoint of transparency, organic ultraviolet absorbing agents are preferred.The organic ultraviolet absorbing agent is not particularly limited, but for example, cyclic imino ester type, benzotriazole type, benzophenone type, etc. are included.From the viewpoint of durability, cyclic imino ester type and benzotriazole type are more preferred. It is also possible to use two or more types of ultraviolet absorbents in combination.

[0018] Particles may be blended into the polyester film for the main purpose of imparting easy slippage and preventing scratches during each process. The type of particles to be blended is not particularly limited as long as it is a particle capable of imparting easy slippage, and specific examples include inorganic particles such as silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, magnesium phosphate, kaolin, aluminum oxide, and titanium oxide, and organic particles such as acrylic resin, styrene resin, urea resin, phenolic resin, epoxy resin, and benzoguanamine resin. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

[0019] The shape of the particles to be used is not particularly limited, and any of spherical, block, rod-like, flat, etc. may be used. There is also no particular restriction on the hardness, specific gravity, color, etc. Two or more kinds of these particles may be used in combination as necessary.

[0020] The average particle size of the particles is usually 5 μm or less, preferably in the range of 0.01 to 3 μm. If the particle size is 5 μm or less, the surface roughness of the film can be made appropriate, and it is preferable because it does not affect the formation of various functional layers in a later process.

[0021] Furthermore, the content of particles in the polyester film is usually 5% by mass or less, preferably in the range of 0.0003 to 3% by mass. When there are no particles or only a small amount of particles, the film has high transparency and is of good quality, but the slipperiness may be insufficient, so that it may be necessary to take measures such as adding particles to the coating layer to improve the slipperiness. Furthermore, when the particle content is 5% by mass or less, the transparency of the film can be sufficiently ensured. When particles are contained, for example, it is preferable to provide a surface layer and an intermediate layer and to contain particles in the surface layer. In this case, it is more preferable to form a multilayer structure having a surface layer containing particles, an intermediate layer, and a surface layer containing particles in this order.

[0022] The method of adding particles to the polyester film is not particularly limited, and any conventionally known method can be adopted. For example, in the case of a multi-layer polyester film, the particles can be added at any stage of manufacturing the polyester constituting each layer, but it is preferable to add the particles after the completion of the esterification or transesterification reaction.

[0023] In addition to the above-mentioned particles, conventionally known antioxidants, antistatic agents, heat stabilizers, lubricants, dyes, pigments, etc. may be added to the polyester film as necessary.

[0024] The thickness of the polyester film is not particularly limited as long as it is within a range that allows formation of a film, but from the viewpoints of mechanical strength, handleability, productivity, etc., it is usually in the range of 10 to 350 μm, preferably 25 to 250 μm, and more preferably 38 to 125 μm.

[0025] Next, a specific example of the production of a polyester film will be described, but the production method is not limited to the following production example. For example, when producing a biaxially stretched film, a method is preferred in which the dried pellets of the polyester raw material described above are extruded as a molten sheet from a die using an extruder, and then cooled and solidified with a cooling roll to obtain an unstretched sheet. In this case, it is preferred to increase the adhesion between the sheet and the rotating cooling drum in order to improve the flatness of the sheet, and an electrostatic application adhesion method and / or a liquid application adhesion method are preferably used. The unstretched sheet is stretched in a biaxial direction. In this case, the unstretched sheet is first stretched in one direction by a roll or tenter type stretching machine. The stretching temperature is usually 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is usually 2.5 to 7 times, preferably 3.0 to 6 times. Then, the film is stretched in a direction perpendicular to the first-stage stretching direction. In this case, the stretching temperature is usually 70 to 170° C., and the stretch ratio is usually 3.0 to 7 times, preferably 3.5 to 6 times. Then, the film is subsequently heat-treated at a temperature of 180 to 270° C. under tension or relaxation of 30% or less to obtain a biaxially stretched film. In the above stretching, a method of stretching in one direction in two or more stages can be adopted. In that case, it is preferable to perform the stretching so that the final stretch ratios in both directions are each within the above range.

[0026] Also, a simultaneous biaxial stretching method can be adopted. The simultaneous biaxial stretching method is a method in which the unstretched sheet is simultaneously stretched and oriented in the longitudinal and transverse directions under a temperature controlled condition usually at 70 to 120°C, preferably 80 to 110°C, and the stretching ratio is 4 to 50 times, preferably 7 to 35 times, and more preferably 10 to 25 times in terms of area ratio. The film is then heat-treated under tension or relaxation of 30% or less at a temperature of 170 to 250° C. to obtain a stretched and oriented film. Regarding the simultaneous biaxial stretching device employing the above-mentioned stretching method, a conventionally known stretching method such as a screw method, a pantograph method, or a linear drive method can be employed.

[0027] <Coating layer> The laminated polyester film of the present invention has a coating layer on at least one surface of the polyester film. The coating layer according to the present invention is an easily adhesive layer provided as an intermediate layer between a polyester film and a functional layer such as a hard coat layer in order to improve adhesion therebetween, and has particularly excellent blocking resistance.

[0028] [Crosslinking agent (A)] The coating layer according to the present invention is preferably formed from a coating liquid containing a crosslinking agent (A). The crosslinking agent has the effect of crosslinking the binder resin described below, thereby improving the adhesion between the coating layer and the functional layer even under high temperature and high humidity conditions, and can also improve the adhesion between the coating layer and the polyester film. As the crosslinking agent, various known crosslinking agents can be used, such as a melamine compound, an epoxy compound, a carbodiimide compound, an oxazoline compound, an isocyanate compound, and a silane coupling compound.

[0029] (Melamine compounds) The melamine compound refers to a compound having a melamine skeleton in the compound, and for example, an alkylolated melamine derivative, a compound obtained by reacting an alkylolated melamine derivative with an alcohol to partially or completely etherify it, and a mixture of these can be used. As the alcohol used for the etherification, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butanol, isobutanol, etc. are preferably used. The melamine compound may be either a monomer or a dimer or higher polymer, or a mixture of these may be used. Furthermore, melamine partially co-condensed with urea or the like can also be used. Examples of the melamine compound include hexamethoxymethylolmelamine, pentamethoxymethylmelamine, hexamethoxymethylmelamine, pentamethoxymethylmelamine, hexaethoxymethylmelamine, hexakis-(methoxymethyl)melamine, N,N',N"-trimethyl-N,N',N"-trimethylolmelamine, N,N',N"-trimethylolmelamine, N-methylolmelamine, N,N'-(methoxymethyl)melamine, N,N',N"-tributyl-N,N',N"-trimethylolmelamine, and the like.

[0030] (Epoxy compound (A1)) The epoxy compound is a compound having an epoxy group in the molecule, and examples thereof include epichlorohydrin, ethylene glycol, polyethylene glycol, glycerin, polyglycerin, tris(2-hydroxyethyl) isocyanurate, condensates of bisphenol A with a hydroxyl group or an amino group, polyepoxy compounds, diepoxy compounds, monoepoxy compounds, and glycidylamine compounds. Examples of the polyepoxy compound include sorbitol polyglycidyl ether, polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanate, glycerol polyglycidyl ether, and trimethylolpropane polyglycidyl ether. Examples of diepoxy compounds include neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, resorcinol diglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and polytetramethylene glycol diglycidyl ether. Examples of the monoepoxy compound include allyl glycidyl ether, 2-ethylhexyl glycidyl ether, and phenyl glycidyl ether. Examples of the glycidylamine compound include N,N,N',N'-tetraglycidyl-m-xylylenediamine, 1,3-bis(N,N-diglycidylamino)cyclohexane, and the like. As the epoxy compound, from the viewpoint of improving adhesion, a polyether-based epoxy compound is preferable, and the amount of epoxy groups in the polyether-based epoxy compound is preferably bifunctional, and more preferably trifunctional or more. Among these, at least one selected from the group consisting of sorbitol polyglycidyl ether, polyglycidyl ether, pentaerythritol polyglycidyl ether, and diglycerol polyglycidyl ether is preferable.

[0031] (Carbodiimide compounds) A carbodiimide compound is a compound having a carbodiimide structure, and is a compound having one or more carbodiimide structures in its molecule. From the viewpoint of improving adhesion, a polycarbodiimide compound having two or more carbodiimide structures in its molecule is more preferable.

[0032] The carbodiimide compound can be synthesized by a conventionally known technique, and generally, a condensation reaction of a diisocyanate compound is used. The diisocyanate compound is not particularly limited, and either aromatic or aliphatic diisocyanates can be used. Specific examples of the diisocyanate compound include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexyl diisocyanate, and dicyclohexylmethane diisocyanate.

[0033] The content of the carbodiimide group contained in the carbodiimide compound, in terms of carbodiimide equivalent (weight [g] of the carbodiimide compound for providing 1 mol of the carbodiimide group), is usually in the range of 100 to 1000, preferably 250 to 800, and more preferably 300 to 700. By using it in the above range, the easy adhesion is improved.

[0034] Furthermore, within the scope of the present invention, in order to improve the water solubility or water dispersibility of the polycarbodiimide compound, a surfactant may be added, or a hydrophilic monomer such as a polyalkylene oxide, a quaternary ammonium salt of a dialkylamino alcohol, or a hydroxyalkylsulfonate may be added.

[0035] (Oxazoline compound (A2)) The oxazoline compound is a compound having an oxazoline group in the molecule, and is preferably a polymer containing an oxazoline group. The oxazoline compound can be prepared by polymerization of an addition-polymerizable oxazoline group-containing monomer alone or with other monomers. Examples of the addition-polymerizable oxazoline group-containing monomer include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline, and one or more of these can be used in combination. Among these, 2-isopropenyl-2-oxazoline is suitable because it is easily available industrially. The other monomer is not limited as long as it is a monomer that can be copolymerized with the addition-polymerizable oxazoline group-containing monomer, and examples thereof include (meth)acrylic acid esters such as alkyl (meth)acrylates (alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t-butyl, 2-ethylhexyl, and cyclohexyl groups); unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, styrenesulfonic acid, and salts thereof (sodium salts, potassium salts, ammonium salts, tertiary amine salts, etc.); unsaturated nitriles such as acrylonitrile and methacrylonitrile; (meth)acrylamide, N-alkyl (meth)acrylate, etc. Examples of the monomer include unsaturated amides such as t)acrylamide and N,N-dialkyl(meth)acrylamide (the alkyl group can be a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a 2-ethylhexyl group, a cyclohexyl group, and the like); vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; α-olefins such as ethylene and propylene; halogen-containing α,β-unsaturated monomers such as vinyl chloride and vinylidene chloride; and α,β-unsaturated aromatic monomers such as styrene and α-methylstyrene. One or more of these monomers can be used. The oxazoline compound may have a polyalkylene oxide chain such as a polyethylene oxide chain, and for example, a (meth)acrylate having a polyalkylene oxide chain may be used as the other monomer. From the viewpoint of improving adhesion, the amount of oxazoline groups in the oxazoline compound is preferably in the range of 0.5 to 10 mmol / g, more preferably 1 to 9 mmol / g, further preferably 3 to 8 mmol / g, and particularly preferably 4 to 6 mmol / g.

[0036] (Isocyanate compounds) The isocyanate compound is a compound having an isocyanate derivative structure, typically an isocyanate or a blocked isocyanate. Examples of the isocyanate include aromatic isocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, and naphthalene diisocyanate; aliphatic isocyanates having an aromatic ring such as α,α,α',α'-tetramethylxylylene diisocyanate; aliphatic isocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic isocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, methylene bis(4-cyclohexyl isocyanate), and isopropylidenedicyclohexyl diisocyanate. Further, polymers and derivatives of these isocyanates such as biuretized products, isocyanurate products, uretdione products, and carbodiimide modified products are also included. These may be used alone or in combination of two or more kinds. Among the above-mentioned isocyanates, aliphatic isocyanates or alicyclic isocyanates are more preferable than aromatic isocyanates in order to prevent yellowing due to ultraviolet rays.

[0037] When used in the form of a blocked isocyanate, examples of the blocking agent include bisulfites, phenolic compounds such as phenol, cresol, and ethylphenol; alcohol compounds such as propylene glycol monomethyl ether, ethylene glycol, benzyl alcohol, methanol, and ethanol; active methylene compounds such as methyl isobutanoylacetate, dimethyl malonate, diethyl malonate, methyl acetoacetate, ethyl acetoacetate, and acetylacetone; mercaptan compounds such as butyl mercaptan and dodecyl mercaptan; lactam compounds such as ε-caprolactam and δ-valerolactam; amine compounds such as diphenylaniline, aniline, and ethyleneimine; acid amide compounds such as acetanilide and acetic acid amide; and oxime compounds such as formaldehyde, acetaldoxime, acetoneoxime, methyl ethyl ketoneoxime, and cyclohexanoneoxime. These may be used alone or in combination of two or more.

[0038] The isocyanate compound may be used alone or as a mixture or bond with various polymers. In terms of improving the dispersibility and crosslinking property of the isocyanate compound, it is preferable to use a mixture and / or bond with a polyester resin or a urethane resin.

[0039] (Silane coupling compound) A silane coupling compound is an organosilicon compound that has an organic functional group and a hydrolyzable group such as an alkoxy group in one molecule. Examples of the silane coupling compound include epoxy group-containing compounds such as 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; vinyl group-containing compounds such as vinyltrimethoxysilane and vinyltriethoxysilane; styryl group-containing compounds such as p-styryltrimethoxysilane and p-styryltriethoxysilane; (meth)acrylic group-containing compounds such as 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloxypropylmethyldimethoxysilane, and 3-(meth)acryloxypropylmethyldiethoxysilane; 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-( amino group-containing compounds such as N-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, 3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, and N-phenyl-3-aminopropyltriethoxysilane; isocyanurate group-containing compounds such as tris(trimethoxysilylpropyl)isocyanurate and tris(triethoxysilylpropyl)isocyanurate; and mercapto group-containing compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, and 3-mercaptopropylmethyldiethoxysilane.

[0040] The crosslinking agent preferably contains an epoxy compound (A1). Compared with other crosslinking agents, epoxy compounds have a smaller bonding selectivity with compounds contained in the polyester film or functional layer, and therefore have the advantage of being easy to use as a constituent material for an easily adhesive coating layer. In addition, when use is assumed not only at room temperature but also in harsh environments such as high temperature and high humidity, the use of an epoxy compound as a crosslinking agent can provide good adhesion between the coating layer and the functional layer, and between the coating layer and the polyester film. However, epoxy compounds have a particularly high activation energy, and unreacted sites of crosslinking agents such as monomers that are constituent units of binder resins and low-molecular-weight reactive compounds remain in the coating layer, and the remaining unreacted sites tend to be easily exposed on the surface of the coating layer. If the remaining unreacted sites are exposed on the surface of the coating layer, films that are wound into rolls and come into contact with each other during the manufacturing and processing process or storage may stick to each other, causing blocking. Therefore, in order to reduce the remaining unreacted sites exposed on the surface of the coating layer, it is necessary to make the surface elastic modulus of the coating layer greater than a specific value. One method for increasing the surface elastic modulus of the coating layer above a specific value is to include an acid catalyst, which will be described later, in the coating liquid that forms the coating layer. This reduces the activation energy during the crosslinking reaction of the epoxy compound and allows the crosslinking reaction to proceed sufficiently, making it possible to achieve excellent blocking resistance even when an epoxy compound is used.

[0041] When the coating layer is formed using a coating liquid, the content of the crosslinking agent in the total non-volatile components in the coating liquid is usually in the range of 0.1 to 90 mass%, preferably 1 to 70 mass%, more preferably 10 to 50 mass%, and even more preferably 20 to 40 mass%. When the content of the crosslinking agent is within the above range, the adhesion between the coating layer and the functional layer is good, and the surface elasticity and surface hardness of the coating layer can be set within the desired range.

[0042] The content of the epoxy compound (A1) in the total crosslinking agent is preferably from 1 to 100 mass%, more preferably from 10 to 90 mass%, even more preferably from 30 to 80 mass%, and even more preferably from 50 to 75 mass%. When the content of the epoxy compound is within the above range, the surface hardness and surface elasticity of the coating layer can be set within the desired range, the adhesion between the coating layer and the functional layer can be improved, and the adhesion between the coating layer and the polyester film can also be improved. In addition, within this range, the activation energy of the crosslinking agent can be reduced by the acid catalytic action described below, and the surface elasticity of the coating layer can be made greater than a specific value.

[0043] The crosslinking agent (A) preferably contains an epoxy compound (A1), more preferably contains one or more selected from the epoxy compound (A1) and the oxazoline compound (A2), and further preferably contains an epoxy compound (A1) and an oxazoline compound (A2). When the crosslinking agent (A) contains an epoxy compound (A1) and an oxazoline compound (A2), the content ratio of the epoxy compound (A1) to the oxazoline compound (A2), (A1) / (A2), is preferably 95 / 5 to 5 / 95, more preferably 80 / 20 to 20 / 80, and further preferably 80 / 20 to 50 / 50.

[0044] [Binder resin (B)] The resin composition for forming the coating layer according to the present invention preferably contains a binder resin (B). As a suitable example of the binder resin, one or more compounds selected from the group consisting of polyurethane resins, polyester resins, and acrylic resins that impart easy adhesion properties can be mentioned.

[0045] (Polyurethane resin) The polyurethane resin is a polymeric compound having a urethane bond in the molecule, and is preferably water-dispersible or water-soluble. The polyurethane resin may be used alone or in combination of two or more kinds.

[0046] In order to impart water dispersibility or water solubility, it is common and preferable to introduce hydrophilic groups such as hydroxyl groups, carboxyl groups, sulfonic acid groups, sulfonyl groups, phosphoric acid groups, ether groups, etc., into the urethane resin. Among the hydrophilic groups, carboxyl groups and sulfonic acid groups are particularly preferable from the viewpoint of improving adhesion.

[0047] One method for producing polyurethane resin is by reacting a hydroxyl group-containing compound with an isocyanate compound. As the hydroxyl group-containing compound used as a raw material, polyol is preferably used, for example, polyether polyols, polyester polyols, polycarbonate polyols, polyolefin polyols, and acrylic polyols. These compounds may be used alone or in combination.

[0048] Examples of polyether polyols include polyethylene glycol, polypropylene glycol, polyethylene propylene glycol, polytetramethylene ether glycol, and polyhexamethylene ether glycol.

[0049] Examples of polyester polyols include polycarboxylic acids (malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, fumaric acid, maleic acid, terephthalic acid, isophthalic acid, etc.) or their acid anhydrides and polyhydric alcohols (ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 2 ... methyl-2,4-pentanediol, 2-methyl-2-propyl-1,3-propanediol, 1,8-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, 1,9-nonanediol, 2-methyl-1,8-octanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-butyl-2-hexyl-1,3-propanediol, cyclohexanediol, bishydroxymethylcyclohexane, dimethanolbenzene, bishydroxyethoxybenzene, alkyldialkanolamines, lactonediols, etc.

[0050] Examples of polycarbonate-based polyols include polycarbonate diols obtained by dealcoholization reaction of polyhydric alcohols with dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate, etc., such as poly(1,6-hexylene) carbonate and poly(3-methyl-1,5-pentylene) carbonate.

[0051] Of the above-mentioned hydroxyl group-containing compounds used to obtain the polyurethane resin, polyester polyols are preferred.

[0052] Examples of polyisocyanate compounds used to obtain polyurethane resins include aromatic diisocyanates such as tolylene diisocyanate, xylylene diisocyanate, methylene diphenyl diisocyanate, phenylene diisocyanate, naphthalene diisocyanate, and tolidine diisocyanate; aliphatic diisocyanates having an aromatic ring such as α,α,α',α'-tetramethyl xylylene diisocyanate; aliphatic diisocyanates such as methylene diisocyanate, propylene diisocyanate, lysine diisocyanate, trimethylhexamethylene diisocyanate, and hexamethylene diisocyanate; and alicyclic diisocyanates such as cyclohexane diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, and isopropylidenedicyclohexyl diisocyanate. These may be used alone or in combination.

[0053] A chain extender may be used when synthesizing the polyurethane resin. The chain extender is not particularly limited as long as it has two or more active groups that react with an isocyanate group, and generally, a chain extender having two hydroxyl groups or two amino groups can be mainly used.

[0054] Examples of chain extenders having two hydroxyl groups include glycols such as aliphatic glycols, such as ethylene glycol, propylene glycol, and butanediol; aromatic glycols, such as xylylene glycol and bishydroxyethoxybenzene; and ester glycols, such as neopentyl glycol hydroxypivalate.

[0055] Examples of chain extenders having two amino groups include aromatic diamines such as tolylenediamine, xylylenediamine, and diphenylmethanediamine; aliphatic diamines such as ethylenediamine, propylenediamine, hexanediamine, 2,2-dimethyl-1,3-propanediamine, 2-methyl-1,5-pentanediamine, trimethylhexanediamine, 2-butyl-2-ethyl-1,5-pentanediamine, 1,8-octanediamine, 1,9-nonanediamine, and 1,10-decanediamine; and alicyclic diamines such as 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, dicyclohexylmethanediamine, 1,4-diaminocyclohexane, and 1,3-bisaminomethylcyclohexane.

[0056] In order to impart water dispersibility or water solubility, a method in which a carboxyl group is introduced into the urethane skeleton using dimethylolpropionic acid, dimethylolbutanoic acid, or the like, and then neutralized with a basic compound to hydrophilize the urethane resin is also preferably used.

[0057] (polyester resin) The polyester resin may be composed mainly of polyvalent carboxylic acids and polyvalent hydroxy compounds such as those shown below. That is, examples of polyvalent carboxylic acids that can be used include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, pyromellitic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, trimellitic acid monopotassium salt, and ester-forming derivatives thereof. Examples of polyhydric hydroxy compounds include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 2-methyl-1,5-pentanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, p-xylylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolethylsulfonate, potassium dimethylolpropionate, etc. One or more of these polyhydric carboxylic acids and polyhydric hydroxy compounds may be appropriately selected, and a polyester resin may be synthesized by a conventional polycondensation reaction.

[0058] In order to impart water dispersibility or water solubility, a method is also preferably used in which sulfoisophthalic acid is used as a copolymerization component as part of the above-mentioned polycarboxylic acid to introduce a sulfonic acid group into the polyester skeleton, and then neutralized with a basic compound to hydrophilize the polyester resin. The amount of copolymerization is usually 1 to 10 mol %, preferably 2 to 8 mol %, based on the total amount of polycarboxylic acid. By introducing an appropriate amount of sulfonic acid groups, the water dispersion stability can be further improved.

[0059] (Acrylic resin) The acrylic resin is a polymer made of polymerizable monomers including acrylic and methacrylic monomers. These may be homopolymers or copolymers, or copolymers with polymerizable monomers other than acrylic and methacrylic monomers. Also included are copolymers of these polymers with other polymers (such as polyesters and polyurethanes). For example, block copolymers and graft copolymers. That is, the acrylic resin may be an acrylic-modified polyester resin or an acrylic-modified polyurethane resin. Also included are polymers (or mixtures of polymers, as the case may be) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in a polyester solution or polyester dispersion. Similarly, polymers (or mixtures of polymers, as the case may be) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in a polyurethane solution or polyurethane dispersion. Similarly, polymers (or mixtures of polymers, as the case may be) obtained by polymerizing polymerizable monomers having carbon-carbon double bonds in other polymer solutions or dispersions are also included. In order to further improve adhesion to polyester films, the resin may contain a hydroxyl group or an amino group.

[0060] The polymerizable monomer having a carbon-carbon double bond is not particularly limited, but particularly representative compounds include various carboxyl group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, maleic acid, and citraconic acid, and salts thereof; various hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, monobutylhydroxyfumarate, and monobutylhydroxyitaconate; methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, lauryl (meth)acrylate, and the like. various nitrogen-containing compounds such as (meth)acrylamide, diacetone acrylamide, or (meth)acrylonitrile; nitrogen-containing compounds containing a hydroxyl group such as N-methylol (meth)acrylamide; various styrene derivatives such as styrene, α-methylstyrene, divinylbenzene, and vinyltoluene; various vinyl esters such as vinyl propionate; various silicon-containing polymerizable monomers such as γ-methacryloxypropyltrimethoxysilane and vinyltrimethoxysilane; phosphorus-containing vinyl monomers; various vinyl halides such as vinyl chloride and vinylidene chloride; and various conjugated dienes such as butadiene.

[0061] Among the above, polymers obtained by polymerizing polymerizable monomers including acrylic and methacrylic monomers are preferred, and it is more preferred that the polymerizable monomers include alkyl (meth)acrylic esters. In addition, when the coating liquid is an aqueous system, from the viewpoint of making it easy to dissolve or disperse the binder resin, it is preferable that the polymerizable monomer has a hydrophilic group such as a hydroxyl group or a carboxyl group. Therefore, the acrylic resin is also preferably a polymer obtained by polymerizing a polymerizable monomer including an alkyl (meth)acrylic acid ester and a hydrophilic group-containing monomer such as a hydroxyl group-containing monomer or a carboxyl group-containing monomer. The acrylic resin may also be an emulsion polymer obtained by polymerizing a polymerizable monomer in the presence of a surfactant.

[0062] As the binder resin, from the viewpoints of adhesion between the coating layer and the polyester film and the functional layer, and the surface elastic modulus and surface hardness of the coating layer, it is preferable to use one or more types selected from polyester resins and urethane resins, and from the viewpoint of adhesion to the polyester film, it is more preferable to use a polyester resin alone.

[0063] When a coating layer is formed using a coating liquid for forming the coating layer, the content of the binder resin (B) in the total non-volatile components in the coating liquid is usually in the range of 10 to 90 mass %, preferably 30 to 80 mass %, and more preferably 50 to 70 mass %. When the content of the binder resin (B) is within the above range, the surface elastic modulus and surface hardness of the coating layer fall within the desired range, the blocking resistance is improved, and the adhesion between the coating layer and the functional layer is improved.

[0064] [Acid catalyst (C)] In the present invention, one of the methods for making the surface elastic modulus of the coating layer greater than 6.0 GPa is to add an acid catalyst (C) to the coating solution for forming the coating layer.

[0065] The acid catalyst is not particularly limited, and examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; oxalic acid, acetic acid, formic acid, phosphoric acid, methanesulfonic acid, trifluoromethanesulfonic acid, isoprene sulfonic acid, camphorsulfonic acid, hexanesulfonic acid, octane sulfonic acid, nonanesulfonic acid, decane sulfonic acid, hexadecanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, cumenesulfonic acid, dodecylbenzenesulfonic acid, naphthalenesulfonic acid, dinonylnaphthalene disulfonic acid, dinonylnaphthalene (mono)sulfonic acid, methyl acid phosphate, ethyl acid phosphate, propyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, butoxyethyl acid phosphate, octyl acid phosphate, 2-ethylhexyl acid phosphate, decyl acid phosphate, and lauryl acid phosphate. Examples of the organic acids include stearyl acid phosphate, oleyl acid phosphate, behenyl acid phosphate, phenyl acid phosphate, nonylphenyl acid phosphate, cyclohexyl acid phosphate, phenoxyethyl acid phosphate, alkoxypolyethylene glycol acid phosphate, bisphenol A acid phosphate, dimethyl acid phosphate, diethyl acid phosphate, dipropyl acid phosphate, diisopropyl acid phosphate, dibutyl acid phosphate, dioctyl acid phosphate, di-2-ethylhexyl acid phosphate, dilauryl acid phosphate, distearyl acid phosphate, diphenyl acid phosphate, and bisnonylphenyl acid phosphate; sulfonium salts, benzothiazolium salts, ammonium salts, and phosphonium salts. These may be used alone or in combination of two or more.

[0066] From the viewpoint of compatibility with the crosslinking agent, it is preferable to use organic acids as the acid catalyst. Among them, from the viewpoint of catalytic activity and cost, an acid catalyst having a sulfonic acid group or a phosphoric acid group is more preferable, and specifically, one or more selected from p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid, dinonylnaphthalene (mono)sulfonic acid, and dodecylbenzenesulfonic acid are more preferable. These acid catalysts may be hydrates or neutralized products of the hydrates.

[0067] When the coating layer is formed from a coating liquid, the content of the acid catalyst in the total non-volatile components in the coating liquid is usually in the range of 0.01 to 10 mass%, preferably 0.1 to 5 mass%, more preferably 0.3 to 3 mass%, and even more preferably 0.5 to 1.5 mass%. When the content of the acid catalyst is within the above range, the compatibility with the crosslinking agent is good, and the catalytic activity is sufficient. In addition, within this range, the activation energy of the crosslinking agent can be reduced, so that the surface elastic modulus of the coating layer can be made greater than a specific value.

[0068] [Other ingredients (D)] In the coating solution for forming the coating layer according to the present invention, particles can be used in combination for the purpose of improving blocking resistance, slippage, etc., within the scope of the present invention. The content of particles in the total non-volatile components in the coating liquid is preferably 0.1 to 20 mass %, more preferably 1 to 18 mass %, and further preferably 3 to 15 mass %. In addition to the above components, additives such as reaction regulators, adhesion enhancers, surfactants, and antistatic agents may be appropriately added.

[0069] [solvent] The coating solution for forming the coating layer is used as a liquid coating solution by incorporating a solvent therein, and the coating solution is applied to the polyester film, and then dried and cured as necessary to form the coating layer. The coating liquid for forming the coating layer may be prepared by dissolving or dispersing a resin composition containing a crosslinking agent, a binder resin, an acid catalyst, etc. in a solvent to form a solution or dispersion. The coating liquid for forming the coating layer may be prepared by dissolving or dispersing a binder resin in a solvent in advance, and mixing the binder resin solution or dispersion with a resin composition containing a crosslinking agent, a binder resin, an acid catalyst, etc. to form a solution or dispersion. The solvent is not particularly limited, and either water or an organic solvent may be used, but from the viewpoint of environmental protection, it is preferable to use an aqueous coating liquid containing water as the main solvent (50% by mass or more). The water content is preferably 60% by mass or more, more preferably 70% by mass or more. The aqueous coating liquid may contain a small amount of an organic solvent. The specific amount of the organic solvent is preferably less than that of water on a mass basis, and is, for example, less than 30% by mass, preferably less than 20% by mass, more preferably less than 10% by mass in the solvent. Examples of organic solvents used in combination with water include alcohols such as ethanol, isopropanol, ethylene glycol, and glycerin, ethers such as ethyl cellosolve, t-butyl cellosolve, propylene glycol monomethyl ether, and tetrahydrofuran, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, and amines such as dimethylethanolamine. These can be used alone or in combination. By appropriately selecting and adding these organic solvents to the aqueous coating liquid as necessary, the stability and coatability of the coating liquid may be improved.

[0070] In addition, when an organic solvent is used alone as the above-mentioned solvent, examples of the organic solvent include aromatic hydrocarbons such as toluene, aliphatic hydrocarbons such as hexane, heptane, isooctane, esters such as ethyl acetate, butyl acetate, ketones such as ethyl methyl ketone (MEK), isobutyl methyl ketone, alcohols such as ethanol, 2-propanol, ethers such as diisopropyl ether, dibutyl ether, etc. These may be used alone or in combination, taking into consideration solubility, coatability, boiling point, etc.

[0071] [Method of forming coating layer] The method for forming a coating layer according to the present invention will be described below. The method for forming the coating layer is not particularly limited, and any conventionally known coating method such as reverse gravure coating, direct gravure coating, roll coating, die coating, bar coating, curtain coating, etc. can be used. Alternatively, the coating layer may be formed by in-line coating or off-line coating. The drying and curing conditions for the coating layer are not particularly limited. For example, when a coating layer is formed on a polyester film by offline coating, the heat treatment is usually performed at 80 to 200°C for 3 to 40 seconds, preferably at 100 to 180°C for 3 to 40 seconds. On the other hand, when forming a coating layer on a polyester film by in-line coating, it is usually advisable to carry out heat treatment at 70 to 280°C for 3 to 200 seconds as a guideline. From the viewpoints of suppressing precipitation of oligomers from the polyester film and promoting the progress of the curing reaction of the crosslinking agent, it is more preferable to carry out heat treatment at 120 to 250°C, even more preferably 150 to 220°C, and particularly preferably 170 to 200°C.

[0072] In the present invention, it is preferable to form a coating layer on a polyester film by in-line coating during the film-forming process of the polyester film. In-line coating is a method of coating a coating solution within the polyester film production process; specifically, it is a method of coating a coating solution at any stage from melt extrusion of polyester to stretching, heat setting, and winding up. Usually, the coating is carried out on any of the following: an unstretched sheet obtained by melting and quenching, a uniaxially stretched film that has been stretched, a biaxially stretched film before heat setting, or a film after heat setting and before being wound up. Although not limited to the following, for example, in the case of sequential biaxial stretching, a particularly excellent method is to coat a uniaxially stretched polyester film stretched in the longitudinal direction (machine direction) with a coating liquid, and then stretch the film in the width direction (transverse direction) to obtain a biaxially stretched polyester film. This method has the advantage of being able to simultaneously form the film and the coating layer, and is advantageous in terms of production costs. In addition, since stretching is performed after coating with the coating liquid, the thickness of the coating layer can be changed by the stretching ratio, and thin film coating can be performed more easily than with off-line coating films. Furthermore, by providing a coating layer on the uniaxially stretched polyester film before the biaxial stretching, the coating layer can be stretched together with the polyester film, thereby allowing the coating layer to adhere firmly to the polyester film. Furthermore, in the production of biaxially stretched polyester film, the film can be stretched while holding the ends of the film with clips or the like, thereby restraining the film in the vertical and horizontal directions, and in the heat setting process, the film can be heat-treated without wrinkles, etc., and while maintaining its flatness. Therefore, the crosslinking reaction of the coating layer progresses sufficiently, improving film-forming properties, and enabling the coating layer to adhere more firmly to the polyester film. Furthermore, the surface elastic modulus of the coating layer can be made greater than a specific value, thereby improving blocking resistance and improving performance such as adhesion to various functional layers that may be formed on the coating layer and moist heat resistance.

[0073] When forming a coating layer by in-line coating, it is preferable to produce a laminated polyester film by coating a solution or dispersion (coating liquid) containing the above-mentioned resin composition, the solid content of which is adjusted to approximately 0.1 to 50 mass %, onto a polyester film.

[0074] Regardless of whether off-line coating or in-line coating is used, heat treatment and irradiation with active energy rays such as ultraviolet rays may be used in combination as necessary. The polyester film constituting the laminated polyester film of the present invention may be previously subjected to a surface treatment such as a corona treatment or a plasma treatment.

[0075] The thickness of the coating layer formed on the polyester film is preferably 0.002 μm or more and 1.0 μm or less, more preferably 0.005 μm or more and 0.25 μm or less, and even more preferably 0.02 μm or more and 0.10 μm or less. When the thickness of the coating layer is within the above range, the adhesion between the coating layer and the polyester film and between the coating layer and the functional layer is good.

[0076] <Physical properties of laminated polyester film> In the present invention, the surface elastic modulus (GPa) of the coating layer of the laminated polyester film is greater than 6.0 GPa. By exceeding 6.0 GPa, not only can the precipitation of oligomers be suppressed, but also the blocking resistance can be improved by reducing the number of remaining unreacted sites exposed on the surface of the coating layer. From the above viewpoints, the surface elastic modulus (GPa) of the coating layer of the laminated polyester film is preferably 6.1 GPa or more, more preferably 6.2 GPa or more, and even more preferably 6.3 GPa or more. The upper limit of the surface elastic modulus (GPa) of the coating layer is not particularly limited, but may be, for example, 50 GPa or less, 30 GPa or less, 20 GPa or less, or 10 GPa or less from the viewpoint of adhesion with the functional layer. Methods for making the surface elastic modulus of the coating layer greater than 6.0 GPa include a method of adjusting the composition of the coating layer by adding an acid catalyst to the coating liquid that forms the coating layer, and a method of adjusting the heat treatment temperature during production. The surface elasticity of the coating layer can be determined by measuring the surface elasticity according to the method described in the Examples.

[0077] In the present invention, the surface hardness (MPa) of the coating layer is preferably 350 MPa or more, more preferably 370 MPa or more, and even more preferably 380 MPa or more. The upper limit of the surface hardness (MPa) of the coating layer is not particularly limited, but may be, for example, 900 MPa or less or 800 MPa or less from the viewpoint of adhesion with the functional layer. If the thickness falls within the above range, defects due to scratches or scraping of the coating layer during the manufacturing and processing processes can be suppressed, and adhesion to the functional layer can be improved. The surface hardness of the coating layer can be determined by measuring the surface hardness using the method described in the Examples.

[0078] In evaluating the blocking resistance of a laminated polyester film, it can be said that the smaller the peel load, the better the blocking resistance. The peel load is preferably 1000 g / cm or less, more preferably 500 g / cm or less, even more preferably 200 g / cm or less, and even more preferably 150 g / cm or less. The lower limit is not particularly limited, but is 0 g / cm or more. The peel load can be specifically determined by measurement using the method described in the Examples.

[0079] The amount of oligomer (cyclic ester trimer) precipitated on the polyester film surface of the laminated polyester film (mg / m 2 ) is 8.0 × 10 -5 mg / m 2 It is preferable that the value is less than 7.5×10 -5 mg / m 2 More preferably, it is 7.0×10 or less. -5 mg / m 2 It is even more preferable that: There is no particular lower limit, but the lower the better. 2 That's all. The amount of oligomer (cyclic ester trimer) precipitated on the surface of the polyester film can be determined by measuring the amount of oligomer (cyclic ester trimer) precipitated on the surface of the polyester film using the method described in the Examples.

[0080] The micro heat of fusion peak temperature of the laminated polyester film of the present invention is preferably 160°C or more and 210°C or less, more preferably 170°C or more and 200°C or less, and even more preferably 175°C or more and 190°C or less. Here, the micro-fusion heat peak temperature is correlated with the heat treatment temperature during production; the higher the heat treatment temperature, the higher the micro-fusion heat peak temperature; and the lower the heat treatment temperature, the lower the micro-fusion heat peak temperature. Within the above range, it is possible to suppress the precipitation of oligomers and to achieve good adhesion at the same time. The minute heat of fusion peak temperature can be specifically determined by measurement using the method described in the Examples.

[0081] The components in the coating layer can be analyzed by, for example, TOF-SIMS, ESCA, fluorescent X-rays, or the like. EXAMPLES

[0082] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples without departing from the gist of the present invention. The measurement and evaluation methods used in the present invention are as follows.

[0083] <Measurement and evaluation methods> (1) Intrinsic viscosity of polyester 1 g of polyester from which components incompatible with the polyester had been removed was precisely weighed, dissolved in 100 mL of a mixed solvent of phenol / tetrachloroethane = 50 / 50 (mass ratio), and measured at 30°C.

[0084] (2) Average particle size The coating layer was observed using a transmission electron microscope (TEM) (Hitachi High-Tech H-7650, accelerating voltage 100 kV), and the average particle size of 10 particles was determined as the average particle size.

[0085] (3) Coating layer thickness The surface of the coating layer was stained with RuO4 and embedded in epoxy resin. Then, sections prepared by ultrathin sectioning were stained with RuO4, and the cross-section of the coating layer was measured using a transmission electron microscope (TEM) (Hitachi High-Technologies Corporation, H-7650, accelerating voltage 100 kV).

[0086] (4) Surface elasticity and surface hardness of the coating layer For the measurement, a nanoindenter "Triboindenter TI980" manufactured by Bruker was used. A drop of "Aron Alpha" (registered trademark) Professional Impact Resistant manufactured by Toagosei Co., Ltd. was applied to a glass slide, and the polyester film side, which is the base material of the laminated polyester film, was fixed to the glass slide side via instant adhesive. In order to fix the glass slide and the mounting stage, correction fluid was applied to the back of the glass slide, which was then placed on the device stage and fixed. The surface elastic modulus (GPa) and surface hardness (MPa) were measured with the coating layer side as the measurement surface. Measurement mode: Load control Maximum load: 10μN Hold time when maximum load is reached: 2 seconds Loading speed, unloading speed: 2μN / sec Measurement temperature: 23℃ Nanoindenter indenter: Berkovich indenter with a triangular pyramid shape and a tip angle of 142° (Bruker, model number: TI-0039)

[0087] (5) Evaluation of blocking resistance Two laminated polyester films to be measured were prepared, and the sides with the easily adhesive coating layer were placed together. An area of ​​12 cm x 10 cm was measured and heated at 40°C, 80% RH, and 10 kg / cm 2 The pressing was carried out under the conditions of 100° C., 20 hours. Thereafter, the films were peeled from each other in accordance with the method specified in ASTM D1893, and the peel load (g / cm) was measured. In general, the adhesion between a coating layer and a polyester film is called blocking property. However, assuming a case where coating layers are provided on both sides of a polyester film, the blocking property was measured between the coating layers.

[0088] (6) Amount of oligomer (cyclic ester trimer) precipitated on the surface of polyester film The laminated polyester film obtained in each example was cut into a box shape measuring 10 cm in length and width and 3 cm in height, with the top open, and the measurement surface (the polyester film side opposite the coating layer) facing inside. Next, 4 mL of DMF (dimethylformamide) was placed in the box prepared by the above method and left to stand for 3 minutes, after which the DMF was recovered and fed to a liquid chromatograph (Shimadzu Corporation: LC-7A, mobile phase A: acetonitrile, mobile phase B: 2% acetic acid aqueous solution, column: Mitsubishi Chemical Corporation "MCI GEL ODS 1HU", column temperature: 40°C, flow rate: 1 mL / min, detection wavelength: 254 nm) to determine the amount of ester cyclic trimer in the DMF, and this value was divided by the area of ​​the film contacted with the DMF to obtain the amount of oligomer (ester cyclic trimer) (mg / m2) on the polyester film surface of the laminated polyester film. 2 The amount of cyclic ester trimers in DMF was determined from the peak area ratio between the standard sample peak area and the measured sample peak area (absolute calibration curve method). The standard sample was prepared by accurately weighing a previously separated ester cyclic trimer and dissolving it in an accurately weighed amount of DMF.

[0089] (7) Formation of hard coat layer A mixed coating solution of 80 parts by mass of KAYARAD DPHA (manufactured by Nippon Kayaku Co., Ltd.), 20 parts by mass of KAYARAD R-128H (manufactured by Nippon Kayaku Co., Ltd.), 5 parts by mass of a photopolymerization initiator (product name: Irgacure 651, manufactured by BASF) and 230 parts by mass of toluene was applied to the coating layer surface of the laminated polyester film obtained in each example so that the dry film thickness was 5 μm, and the coating was dried at 80° C. for 1 minute to remove the solvent, and then ultraviolet rays were applied at 250 mJ / cm 2 The coating layer was cured by irradiation to form a hard coat layer on the coating layer.

[0090] (8) Adhesion to hard coat layer The laminated polyester film with hard coat layer obtained in (7) above was left in an environment of 60°C and 90% RH for 24 hours, after which cross-cuts were made so that there were 100 grids per inch, and an 18 mm wide tape (Cellotape (registered trademark) CT-18, manufactured by Nichiban Co., Ltd.) was applied on top of the cross-cuts, which were then rapidly peeled off at a peel angle of 180°. The peeled surface was observed and evaluated based on the peeled area. The evaluation criteria were as follows. If the peeled area was less than 50%, there was no problem in practical use. ◎(Excellent): Peeling area less than 10% Good: Peeling area 10% or more but less than 50% ×(poor): Peeling area 50% or more

[0091] (9) Micro-fusion heat peak temperature A measurement sample (5 mg) was prepared using the laminated polyester film obtained in each example, and the small heat of fusion peak was measured using a differential scanning calorimeter (PerkinElmer, model DSC8500) in accordance with JIS K7121 (1999) by the following method. The sample was measured at a temperature range of 25° C. to 300° C. at a heating rate of 20° C. / min. The apex of a small peak observed at this time, which is lower than the apex temperature of the endothermic peak attributed to the melting of the sample and exists near the endothermic peak, or the apex of a small shoulder observed in the endothermic peak, was determined as the small heat of fusion peak (° C.).

[0092] <Materials used> The method for producing the polyester used in the present invention is described below.

[0093] [Production method of polyester (1)] 100 parts by mass of dimethyl terephthalate and 55 parts by mass of ethylene glycol were used as starting materials, and 0.04 parts by mass of magnesium acetate tetrahydrate was added as a catalyst to a reactor. The reaction was started at 150°C, and the reaction temperature was gradually increased as methanol was distilled off, reaching 230°C after 3 hours. After 4 hours, the transesterification reaction was essentially complete. 0.02 parts by mass of ethyl acid phosphate was added to this reaction mixture, and then 0.04 parts by mass of antimony trioxide was added, and the polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually increased from 230°C to 280°C. Meanwhile, the pressure was gradually reduced from normal pressure to 0.3 mmHg. After the start of the reaction, the reaction was stopped at the point corresponding to an intrinsic viscosity of 0.65 dL / g due to a change in the stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain polyester (1) with an intrinsic viscosity of 0.65 dL / g.

[0094] [Production method of polyester (2)] 100 parts by mass of dimethyl terephthalate and 45 parts by mass of ethylene glycol were used as starting materials, and 0.06 parts by mass of magnesium acetate tetrahydrate was added to the reactor as a catalyst. The reaction was started at 150°C, and the reaction temperature was gradually increased as methanol was distilled off, reaching 230°C after 3 hours. After 4 hours, the transesterification reaction was essentially completed. 0.03 parts by mass of ethyl acid phosphate was added to this reaction mixture, and then 0.3 parts by mass of silica particles with an average particle size of 2.7 μm dispersed in ethylene glycol and 0.03 parts by mass of antimony trioxide were added, and the polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually increased from 230°C to 280°C. Meanwhile, the pressure was gradually reduced from normal pressure, and finally reached 0.3 mmHg. After the start of the reaction, the reaction was stopped at the point corresponding to an intrinsic viscosity of 0.65 dL / g due to changes in the stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure to obtain polyester (2) with an intrinsic viscosity of 0.65 dL / g.

[0095] The following coating solution was used to form the coating layer. [(A) Crosslinking agent] (A1): Epoxy compound Water-soluble polyglycerol polyglycidyl ether (A2): Oxazoline compound Acrylic polymer having oxazoline groups and polyalkylene oxide chains EPOCROS (registered trademark) (oxazoline group amount = 4.5 mmol / g, manufactured by Nippon Shokubai Co., Ltd.)

[0096] [(B) Binder resin] (B1): Aqueous dispersion of polyester resin copolymerized with the following composition (Dicarboxylic acid components) terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid = 56 / 40 / 4 (mol%) (Diol components) Ethylene glycol / 1,4-butanediol / diethylene glycol = 70 / 20 / 10 (mol%) (B2): Water dispersion of polyester resin copolymerized with the following composition (Dicarboxylic acid component) 2,6-naphthalenedicarboxylic acid / 5-sodium sulfoisophthalic acid = 92 / 8 (mol%) (Diol component) Ethylene glycol / diethylene glycol = 80 / 20 (mol%)

[0097] [(C) Acid catalyst] (C1): Dinonylnaphthalene(mono)sulfonic acid (DNNSA) (C2): p-Toluenesulfonic acid monohydrate (p-TSA) (manufactured by Nacalai Tesque, Inc.) (C3): p-Toluenesulfonic acid, ammonia neutralized (p-TSA neutralized)

[0098] [(D) Other ingredients] (D1): Zirconium oxide particles with an average particle size of 15 nm (D2): Silica sol with an average particle size of 0.14 μm

[0099] Example 1 A blend of polyester (1) and polyester (2) in a mass ratio of 82:18 was used as the raw material for layer A, and polyester (1) alone was used as the raw material for layer B. These were fed into an extruder, heated and melted at 285°C, and co-extruded to form a layer structure of two types of three layers (A / B / A) with layer A being the outermost layer (surface layer) and layer B being the middle layer, with the thickness composition ratio being A / B / A = 5 / 90 / 5 under the extrusion conditions. The film was then cooled and solidified while being in close contact with a mirror-finished cooling drum with a surface temperature of 40 to 50°C, to produce an unstretched polyethylene terephthalate film. This film was stretched 3.7 times in the longitudinal direction while passing through a group of heated rolls at 85° C., to obtain a uniaxially stretched polyester film. Coating solution 1 shown in Table 1 below was applied to one side of this uniaxially stretched polyester film, and then this film was introduced into a tenter stretching machine and stretched 4.3 times in the width direction at 100°C. Further, it was subjected to heat treatment at 200°C, and then a 2% relaxation treatment in the width direction was performed to obtain a biaxially stretched polyester film (laminated polyester film) having a thickness of 50 μm and a coating layer having a thickness (after drying) of 0.06 μm.

[0100] (Examples 2 to 5) A laminated polyester film was obtained in the same manner as in Example 1, except that the coating layer had a composition shown in Table 1.

[0101] Comparative Example 1 A laminated polyester film was obtained in the same manner as in Example 1, except that the composition of the coating solution was changed to that shown in Table 1.

[0102] The evaluation results of the laminated polyester films obtained in Examples 1 to 5 and Comparative Example 1 are shown in Table 2 below.

[0103] [Table 1]

[0104] [Table 2]

[0105] As shown in Table 2, the laminated polyester film of the present invention has a surface elastic modulus of the highly adhesive coating layer of more than 6.0 GPa, thereby suppressing precipitation of oligomers and exhibiting excellent blocking resistance. The laminated polyester film of the present invention also has excellent adhesion to the functional layer.

Claims

1. A coating layer is provided on at least one surface of the polyester film, the coating layer is formed from a coating liquid containing a crosslinking agent (A) containing an epoxy compound (A1) and an oxazoline compound (A2), an acid catalyst (C), and a binder resin (B); the content ratio (A1) / (A2) of the epoxy compound (A1) to the oxazoline compound (A2) is 80 / 20 to 20 / 80; A laminated polyester film, wherein the coating layer has a surface elastic modulus of more than 6.0 GPa.

2. The laminated polyester film according to claim 1 , wherein the binder resin (B) contains a polyester resin.

3. 3. The laminated polyester film according to claim 1, wherein the micro-melting heat peak temperature is 160° C. or more and 210° C. or less.

4. A coating layer is provided on at least one surface of the polyester film, The coating layer is formed from a coating liquid containing an acid catalyst (C), a binder resin (B), and a crosslinking agent (A), The surface elastic modulus of the coating layer is greater than 6.0 GPa; The binder resin (B) contains a polyester resin, A laminated polyester film having a micro heat of fusion peak temperature of 160°C or higher and 210°C or lower.

5. The laminated polyester film according to claim 4 , wherein the crosslinking agent (A) contains an epoxy compound (A1).

6. The crosslinking agent (A) further contains an oxazoline compound (A2), 6. The laminated polyester film according to claim 5, wherein the content ratio (A1) / (A2) of the epoxy compound (A1) to the oxazoline compound (A2) is 80 / 20 to 20 / 80.

7. The laminated polyester film according to any one of claims 1 to 6, wherein the coating layer has a surface hardness of 370 MPa or more.

8. The laminated polyester film according to any one of claims 1 to 7, wherein the acid catalyst (C) has a sulfonic acid group or a phosphoric acid group.

9. The laminated polyester film according to any one of claims 1 to 8, wherein the acid catalyst (C) is at least one selected from the group consisting of p-toluenesulfonic acid, dinonylnaphthalene disulfonic acid, dinonylnaphthalene (mono)sulfonic acid, and dodecylbenzenesulfonic acid.

10. A coating layer is provided on at least one surface of the polyester film, The coating layer is formed from a coating liquid containing a crosslinking agent (A), a binder resin (B), and an acid catalyst (C), A laminated polyester film having a functional layer, the laminated polyester film having a coating layer, the coating layer having a surface elasticity of more than 6.0 GPa, and a functional layer on the coating layer.

11. A laminated polyester film with a functional layer as described in Claim 10, wherein the crosslinking agent (A) contains an epoxy compound (A1).

12. A laminated polyester film having a functional layer, comprising the laminated polyester film according to any one of claims 1 to 9 and a functional layer on the coating layer.

13. The laminated polyester film with a functional layer according to any one of claims 10 to 12, wherein the functional layer is a hard coat layer.

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